1. Field of the Invention
The present invention relates to the generation of multiple frequencies and more particularly, the present invention relates to a frequency scalable, low self-generated noise frequency source.
2. Description of the Related Art
In a typical communications channel, the phase noise is introduced on the desired signal being received or transmitted. This phase noise degrades the overall signal to noise ratio (SNR), thereby leading to degraded signal acquisition or bit error rate performance. Typically, phase noise is introduced when the signal is multiplied by a local oscillator (LO) signal in a frequency conversion stage, the LO signal being the main source of the phase noise. Multiple frequency conversions in a communications channel and corresponding multiple LO signals may result in significant SNR degradation due to phase noise.
The object of the present invention is to provide a frequency scalable, low self-generated noise frequency source having a modular architecture for generating coherent or mostly-coherent local oscillator signals. The frequency source in accordance with the present invention includes a common reference, a coherent common set of high frequency references and specific local oscillators which may be non-coherent for each specific output frequency. Delay lines may be included in the paths to ensure time delay alignment at the payload level. The use of these elements maximizes design reuse since just the specific IF local oscillators and delays and specific filters need custom design.
A frequency source in accordance with the present invention may include the following elements:
a modular design allowing the generation of multiple coherent local oscillators via replication of the modular design elements;
the use of a common low-frequency reference for all local oscillators;
the generation of a set of higher frequency tones as high frequency reference signals, most economically, via the transfer of an intermediate reference signal to all modules and the local generation of the set of higher frequency reference tones, the set of high frequency reference signals generally being evenly spaced in frequency;
the incorporation of delay elements to time-match all local oscillators;
the generation in each module of an intermediate frequency specific local oscillator signal which is based on the reference but is not fully coherent with respect to the high frequency reference tones;
the generation in each module of the final local oscillator signal by mixing the coherent high-frequency reference signal with the specific IF local oscillator signal, the mixing being either high-side or low-side mixing.